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[vector crypto] Clarifying mandate for vector register index alignment to LMUL/EMUL #1653

Merged
merged 10 commits into from
Nov 26, 2024
1 change: 1 addition & 0 deletions src/scalar-crypto.adoc
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[[crypto_scalar_instructions]]
== Cryptography Extensions: Scalar & Entropy Source Instructions, Version 1.0.1

=== Changelog
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1 change: 1 addition & 0 deletions src/v-st-ext.adoc
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Expand Up @@ -228,6 +228,7 @@ will run. The `vill` bit in `vtype` should be checked after setting
code path should be provided if it is not. Alternatively, a profile
can mandate the minimum SEW at each LMUL setting.

[[vector-register-grouping]]
===== Vector Register Grouping (`vlmul[2:0]`)

Multiple vector registers can be grouped together, so that a single
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19 changes: 14 additions & 5 deletions src/vector-crypto.adoc
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Expand Up @@ -243,8 +243,13 @@ for vector crypto instructions.

[[crypto-vector-instruction-constraints]]
==== Instruction Constraints

All standard vector instruction constraints specified by RVV 1.0 apply to Vector Crypto instructions.
In addition to those constraints a few additional specific constraints are introduced.

The following is a quick reference for the various constraints of specific Vector Crypto instructions.


vl and vstart constraints::
Since `vl` and `vstart` refer to elements, Vector Crypto instructions that use elements groups
(See <<crypto-vector-element-groups>>) require that these values are an integer multiple of the
Expand Down Expand Up @@ -308,8 +313,13 @@ all other `SEW` values are _reserved_.

|===

Source/Destination overlap constraints::
Some Vector Crypto instructions have overlap constraints. Encodings that violate these constraints are _reserved_.
Vector/Scalar constraints::
This specification defines new vector/scalar (.vs) instructions that uses *Scalar Element Groups*. The *Scalar Element Group* operand has `EMUL = ceil(EGW / VLEN)`.

[NOTE]
====
Scalar element group operands do not need to be aligned to LMUL for any implementation with VLEN >= EGW.
====

In the case of the `.vs` instructions defined in this specification, `vs2` holds a 128-bit scalar element group.
For implementations with `VLEN` ≥ 128, `vs2` refers to a single register. Thus, the `vd` register group must not
Expand Down Expand Up @@ -353,7 +363,6 @@ The Vector Crypto Extensions define Vector-Scalar instructions that are similar
Vector Reduction Operations in that they get a scalar operand from a vector register. However, they differ
in that they get a scalar element group
(see <<crypto-vector-element-groups>>)
// link:https://github.com/riscv/riscv-v-spec/blob/master/element_groups.adoc[RISC-V Vector Element Groups])
from `vs2` and they return _vector_ results to `vd`, which is also a source vector operand.
These Vector-Scalar crypto instructions also use the `.vs` suffix in their mnemonics.

Expand Down Expand Up @@ -482,7 +491,7 @@ on _any_ embedded (Zve*) or application ("V") base Vector Extension.
All _cryptography-specific_ instructions defined in this Vector Crypto specification (i.e., those
in <<zvkned>>, <<zvknh,Zvknh[ab]>>, <<Zvkg>>, <<Zvksed>> and <<zvksh>> but _not_ <<zvbb>>,<<zvkb>>, or <<zvbc>>) shall
be executed with data-independent execution latency as defined in the
link:https://github.com/riscv/riscv-crypto/releases/tag/v1.0.1-scalar[RISC-V Scalar Cryptography Extensions specification].
<<#crypto_scalar_instructions,RISC-V Scalar Cryptography Extensions specification>>.
It is important to note that the Vector Crypto instructions are independent of the
implementation of the `Zkt` extension and do not require that `Zkt` is implemented.

Expand Down Expand Up @@ -998,7 +1007,7 @@ GCM/GMAC extension to enable high-performace SM4-GCM.

The Zvkt extension requires all implemented instructions from the following list to be
executed with data-independent execution latency as defined in the
link:https://github.com/riscv/riscv-crypto/releases/tag/v1.0.1-scalar[RISC-V Scalar Cryptography Extensions specification].
<<#crypto_scalar_instructions,RISC-V Scalar Cryptography Extensions specification>>.

Data-independent execution latency (DIEL) applies to all _data operands_ of an instruction, even those that are not a
part of the body or that are inactive. However, DIEL does not apply
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